Hole-opener for enlarging pilot hole

ABSTRACT

The hole-opener is designed so that it can be disassembled in the field to replace worn cones or to enlarge the effective diameter of the tool. It comprises: a tubular drive sub, which connects at its front end with a rotating drill string which is being pulled along a pilot hole; a sleeve which slides over the rear portion of the drive sub; and a retainer sub which is connected with the rear end of the drive sub. The drive sub has external protruding bars which engage slots formed in the forward end of the sleeve, for limiting forward movement of the sleeve and locking the drive sub and sleeve together so that they rotate as a unit. The retainer sub has a radial shoulder which abuts the rear end of the sleeve to lock it in place. The retainer sub also transmits axial pull from the drive sub to the sleeve. The sleeve carries rotary cutting elements which are pulled and rotated to cut formation and enlarge the pilot hole.

FIELD OF THE INVENTION

[0001] The present invention relates to a hole-opener for enlarging thediameter of an underground pilot hole. More particularly it relates to ahole-opener that can easily be disassembled to replace the rotarycutting elements.

BACKGROUND OF THE INVENTION

[0002] In connection with laying cables or installing a flowline it isperiodically necessary to bore a generally horizontal, undergroundborehole extending between one surface location and another. This mightbe done, for example, to provide a borehole at a crossing beneath ariver.

[0003] In such an operation, a relatively small diameter pilot hole isdrilled by a rig. This is done using a string of drill pipe having, atthe drilling end, a fluid-driven motor rotating a drill bit. Once thepilot hole is formed, the bit is replaced with a tool referred to as ahole-opener The drill string is then rotated and pulled to draw thehole-opener back along the pilot hole to enlarge its diameter. Thisprocedure may be repeated more than once with progressively largerhole-openers, to gradually increase the pilot tube diameter to achieve aborehole of the desired size.

[0004] A typical prior art hole-opener is shown in FIG. 1. It comprises:

[0005] a one-piece tubular body forming a through bore and havingthreaded connections at the front and rear ends of the tool;

[0006] ‘arms’ or bars are welded or bolted to the exterior surface ofthe body—they extend longitudinally thereof in parallel,circumferentially spaced apart relationship;

[0007] each arm has at its front end a rotary cutting element, such as atoothed cone mounted on a support pin extending between the arm and thebody;

[0008] jet ports are provided, extending through the side wall of thebody at the cones, for jetting drilling fluid into the annulus formedbetween the tool and drill string and the pilot hole wall to clean thecones and remove drill cuttings; and

[0009] a threaded plug is provided for closing the through bore at thebody's rear end.

[0010] There are shortcomings associated with these commonly used tools.These shortcomings appear to have simply been tolerated for many yearswithout a useful remedy, as far as I am aware.

[0011] More particularly, the cones wear out in use and need to beremoved and replaced. However, it is not practical to make thischange-out in the field with the prior art solid tools.

[0012] In addition, it is therefore necessary to maintain at the site aninventory of complete tools having progressively larger diameters, ifthe pilot hole is to be enlarged in stages.

[0013] It is the objective of the present invention to provide a tool orhole-opener which is improved with respect to these shortcomings.

SUMMARY OF THE INVENTION

[0014] In accordance with the invention, a hole-opener is provided whichincorporates a removable sleeve mounted on a tubular body (referred toas a drive sub). Arms and cutting elements are affixed to the sleeve.Means are provided for locking the drive sub and sleeve together so thatthey rotate as a unit. Means are also provided for locking the sleeveaxially in a pre-determined position on the drive sub. And finally,means are provided for transmitting the pulling force of the drillstring and attached drive sub to the sleeve and its cutting elements.

[0015] In one preferred embodiment, the hole-opener has front and rearends and comprises:

[0016] a tubular drive sub having a longitudinal bore and threadedconnections at each end, more preferably a box at the front end and apin at the second end;

[0017] a tubular sleeve which slides onto the rear end of the drive sub.The sleeve has a plurality of radially protruding arms attached to itsfront end surface at spaced positions about its circumference. A cuttingelement, preferably a toothed cone, is rotatably mounted to the frontend of each arm;

[0018] means for engaging the drive sub and sleeve so that they rotatetogether. More preferably such means comprise outwardly protruding,circumferentially spaced apart stabilizer bars affixed to the externalsurface of the drive sub and extending longitudinally thereof. Thesestabilizer bars engage corresponding slots formed in the front end ofthe sleeve. The bars and slot walls combine to transfer rotational forcefrom the drive sub to the sleeve. The bars also function as a stop, tolimit the axial travel of the sleeve along the drive sub and lock thelatter's front end at a pre-determined position; and

[0019] a retainer sub, which has a threaded connection at its front endfor engaging the rear connection of the drive sub. The retainer sub alsohas a radial shoulder which abuts the rear end face of the sleeve andlocks the sleeve at its rear in the pre-determined position. Theretainer sub also functions to transmit the axial pull force from thedrill string and drive sub to the sleeve and its cutting elements;

[0020] the drive sub forming ports extending through its side wallwhich, when the tool has been assembled, are positioned adjacent thecutting elements and serve to jet drilling fluid so as to clean thecones and remove cuttings through the annulus.

[0021] Broadly stated, the invention is concerned with a hole-opener forenlarging the diameter of a pilot hole, the hole-opener having front andrear ends and comprising: a tubular drive sub having an externalsurface, a longitudinal bore and threaded connections at its front andrear ends; a tubular sleeve for sliding axially over the rear end of thedrive sub; means for locking the sleeve and drive sub together forrotation as a unit; means, carried by the drive sub, for engaging thefront end of the sleeve to stop its axial movement along the drive subat a pre-determined position; a retainer sub for threadably engaging therear end connection of the drive sub and bearing against the rear end ofthe sleeve to lock the sleeve in the pre-determined position; the sleevecarrying at least one rotary cutting element assembly at its front end;the drive sub forming ports for jetting drilling fluid contiguous to thecutting elements when the sleeve is locked in the pre-determinedposition.

DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a perspective sectional side view of a hole-opener inaccordance with the prior art;

[0023]FIG. 2 is a partly sectional side view of an assembled hole-openerin accordance with the present invention;

[0024]FIG. 3 is a sectional side view of the drive sub;

[0025]FIG. 4 is a sectional side view of the retainer sub; and

[0026]FIG. 5 is a sectional side view of the sleeve showing a slot, thearms and rotary cones.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] The tool or hole-opener 1 comprises a drive sub 2, a sleeve 3 anda retainer sub 4.

[0028] ‘Subs’ are used because they are heavy steel tubulars equippedwith threaded pins and boxes adapted to connect with the connections ofdrill pipe commonly used in this service. The subs are adapted to be‘made up’ and ‘broken’ by the rig equipment. However the subs have beenmodified in certain respects, as described below, to prepare them foruse in this tool.

[0029] More particularly, the drive sub 2 has a box connection 5 at itsfront end 6 and a pin connection 7 at its rear end 8. Stabilizer bars 9are welded to the drive sub's external surface 10. These stabilizer bars9 extend longitudinally of the drive sub 2 at spaced positions aroundits circumference. The stabilizer bars 9 are designed to centralize thetool in the pilot hole (not shown). They also function to act as stopslimiting axial advance of the sleeve 3 along the drive sub 2 and as partof the rotary drive connection between the drive sub 2 and sleeve 3. Thedrive sub side wall 11 also forms ports 12, between the stabilizer bars9, for jetting drilling fluid into the annulus formed between the tooland the borehole wall.

[0030] The sleeve 3 is formed with slots 13 in its forward end 14, forreceiving the stabilizer bars 9. The side walls 15 of the slots 13 andthe bars 9 combine to lock the sleeve 3 and drive sub 2 together forrotation as a unit. The sleeve 3 also carries a plurality of outwardlyprotruding arms 16 affixed to the front end of the sleeve's outersurface 17. The arms 16 extend longitudinally of the sleeve 3 in spacedapart arrangement. Each arm 16 carries a rotatably mounted, toothed cone18 at its front end 19. The cones 18 are positioned adjacent the jetports 12.

[0031] The retainer sub 4 has a box connection 20 at its front end,sized to be slidably received in the rear end of the bore 21 of thesleeve 3. The box connection 20 is connected with the pin connection 7of the drive sub 2. The retainer sub 4 also has a radial shoulder 22which abuts the rear end face 23 of the sleeve 2 when the tool isassembled. The retainer sub 4, being threadably engaged with the drivesub 2, therefore functions to transmit axial pull from the drill string24 to the sleeve 3 and its rotary cones 18. In addition, the retainersub shoulder 22 combines with the stabilizer bars 9 to lock the sleeve 3in a pre-determined position with the cones 18 positioned opposite thejet ports 12.

[0032] A plug sub 25 is threaded onto the rear pin connection 26 of theretainer sub 4, to close off its bore 27.

[0033] The resultant tool can be disassembled by backing off andremoving the retainer sub 4 and removing and replacing the sleeve 3.This is done when the cones 18 are worn or are to be replaced to cut alarger diameter borehole.

[0034] It is contemplated that variants of the described tool can beimplemented by those skilled in the art without changing the substanceof the tool. For example, splines can be used to lock the drive sub andsleeve for rotation together. In addition, the tubular retainer sub canbe replaced with a plug—the term ‘retainer sub’ is intended to beinterpreted to include a plug.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A hole-opener forenlarging the diameter of a pilot hole, the hole-opener having front andrear ends and comprising: a tubular drive sub having an externalsurface, a longitudinal bore and threaded connections at its front andrear ends; a tubular sleeve for sliding axially over the rear end of thedrive sub; means for locking the sleeve and drive sub together forrotation as a unit; means, carried by the drive sub, for engaging thefront end of the sleeve to stop its axial movement along the drive subat a pre-determined position; a retainer sub for threadably engaging therear end connection of the drive sub and bearing against the rear end ofthe sleeve to lock the sleeve in the pre-determined position; the sleevecarrying at least one rotary cutting element assembly at its front end;the drive sub forming ports for jetting drilling fluid contiguous to thecutting elements when the sleeve is locked in the pre-determinedposition.
 2. The hole-opener as set forth in claim 1 wherein the drivesub has outwardly protruding, circumferentially spaced apart barsaffixed to its external surface and extending longitudinally thereof andthe front end of the sleeve is slotted to engage the bars to stopforward axial movement of the sleeve and to lock the sleeve and drivesub together for rotation as a unit.
 3. A hole-opener for enlarging thediameter of a pilot hole, the hole-opener having front and rear ends andcomprising: a tubular drive sub having an external surface, alongitudinal bore and threaded connections at its front and rear ends; atubular sleeve mounted on the rear end of the drive sub; means forlocking the sleeve and drive sub together for rotation as a unit; means,carried by the drive sub and engaging the front end of the sleeve, forstopping the sleeve at a pre-determined position; a retainer subthreadably engaging the rear end connection of the drive sub and havinga shoulder bearing against the rear end of the sleeve to lock the sleevein the pre-determined position; the sleeve carrying a plurality ofrotary cutting element assemblies at its front end; the drive subforming ports for jetting drilling fluid contiguous to the cuttingelements.
 4. The hole-opener as set forth in claim 3 wherein the drivesub has outwardly protruding, circumferentially spaced apart barsaffixed to its external surface and extending longitudinally thereof andthe front end of the sleeve forms slots engaging the bars so that thebars cooperate with the retainer sub to lock the sleeve axially in thepre-determined position, the bars and sleeve interlock so that the drivesub and sleeve will rotate as a unit and the drive sub will impartpulling force to the sleeve through the retainer sub.